MLA
Gonne, Maud, 1866-1953. Letter written by Maud Gonne to William Butler Yeats - December 26 [1909]. December 26, 1909. Maud Gonne and W.B. Yeats Papers, circa 1890-1938. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/552w3r24fn-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (December 26, 1909)[Letter written by Maud Gonne to William Butler Yeats - December 26 [1909]]. Maud Gonne and W.B. Yeats Papers, circa 1890-1938, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/552w3r24fn-cor.
Chicago
Gonne, Maud, 1866-1953, Letter written by Maud Gonne to William Butler Yeats - December 26 [1909], December 26, 1909, Maud Gonne and W.B. Yeats Papers, circa 1890-1938, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/552w3r24fn-cor.